The present invention is directed to a dual-rate linear damper which provides greater damping in a second direction than in a first direction. One embodiment provides a significant increase in damping to effectively lock the position of the piston rod in position relative to the housing until a particular breakover force is incurred.
This aspect of the invention is related to the adjustable, lockable devices described and claimed in commonly assigned U.S. patent application Ser. No. 08/424,925 filed Apr. 19, 1995, which application is hereby incorporated by reference.
As noted in the earlier application, a number of applications require a suitable alternative to gas springs which can provide a first damping force in a first linear direction and a significantly greater resistance to movement in the other linear direction. Certain of these applications require the capability to effectively lock the piston relative to the housing until a particular predetermined breakover force is incurred.
Some of these applications include a hold-open rod for clam-shell halves of an engine cowling; the retainer for the door on the overhead luggage compartment in an aircraft cabin; the door covering an aircraft fueling port. While either the resisting or locking embodiments could be used on any of these or other applications, only the fuel door application actually requires the features of the lockable embodiment.
The dual-rate linear damper of the present invention employs a plurality of elastomeric disks mounted on a piston rod, each disk having a backing plate in the form of a metal washer. Preferably, each elastomeric disk has a plurality of relief grooves cut in at least one of its faces to facilitate collapse. In a first, typically expanding direction, the elastomeric disks will fold away from the backing disks and provide only minimal resistance to movement while in the second, typically collapsing direction, the backing plate will reinforce the elastomer and effectively result in bulging of the elastomer into the internal surface of the piston housing. This produces a force resisting movement which is between about five and ten times the resistance to movement in the first direction.
The second embodiment provides a locking mechanism for holding the respective door in the open position unless and until a particular breakover force is incurred to prevent damage to the door. That mechanism includes a first elastomeric spring which bulges laterally outwardly under the influence of a second spring. This embodiment utilizes an actuator mechanism which includes a first actuator rod which extends through the first and second springs; a second short rod portion that is biased by a third spring in a direction away from the first actuator rod; and a manually-operable, a laterally extending lever which enables said biasing of said third spring to be overcome, said second rod portion to be brought into engagement with an end of said rod and said rod to be displaced against the biasing force of said second spring to unload said first spring resulting in said resistance force being significantly reduced, whereby said inner cylindrical member can be moved relative to said outer cylindrical member.
Various features, advantages and characteristics of the present invention will become apparent after a reading of the following detailed description of the preferred embodiments.